Furfural solvent refining and recovery process



.Ily 2l, 1959 D. K. BEAVONA FURFURAL SOLVENT REFINNG AND RECOVRY PROCESSFiled March 29, 1957 United States arent FURFURAL SOLVENT REFINING ANDRECOVERY PROCESS David K. Beavon, Darien, Conn., assigner to Texaco,Inc., a corporation of Delaware Application March 29, 1957, Serial No.649,47 6 9 Claims. (Cl. 208-327) This invention relates to solventrefining. More particularly, this invention relates to a solventrefining process employing liquid furfural as the selective solvent.Still more particularly, this invention relates to a method of operatinga furfural solvent refining process whereby the turfural recovered fromthe resulting raffinate and extract phases contains a reduced amount oflight oils, such as co-boiling aromatic hydrocarbons in the range30G-500 F. and/or a reduced amount of water.

The practice of this invention is particularly applicable to the solventrefining of gas oils, such as virgin gas oils, pipe still gas oils,catalytic cycle gas oils, light and/or heavy gas oils and the like. Inone embodiment the practice of this invention is particularly applicableto the solvent refining of petroleum oils, particularly petroleum oilswhich contain hydrocarbons having a boiling point in the range 30G-500F., more or less, and which are preferentially soluble in furfural. Ithas been observed that in a furfural solvent refining operation theretends to be a buildup of these light aromatic hydrocarbon oils (boilingpoint in the range SOO-500 F.) in the furfural employed as the selectivesolvent. These light oils tend to dilute the furfural, lessen itscapacity and at the same time decrease the gravity differential betweenthe furfural (extract phase) and the refined oil (raffinate phase)thereby making separation between the raffinate phase and the extractphase more difficult.

Accordingly it is an object of this invention to provide an improvedmethod for carrying out a furfural refining operation.

It is another object of this invention to provide an improved method forthe recovery of furfural employed in a solvent refining operation.

Still another object of this invention is to provide in a solventrefining operation an improved method for the recovery of furfural fromthe raliinate and extract phases.

Yet another object of this invention is to provide a method in a solventrefining operation for the recovery of liquid furfural having arelatively reduced amount or concentration (less than equilibrium) ofsubstantially coboiling light oils (boiling point inthe range SOO-500F.) and/ or Water dissolved therein.

How these and other objects of this invention are achieved will becomeapparent in the light of the accompanying disclosure and drawing whereinthere is schematically illustrated a furfural solvent refining processcarried out in accordance with the teachings of this invention.

Referring now in detail to the drawing a solvent relining tower 11,which may be a packed tower, a bubble tray tower for liquid-liquidcontacting, combination of mixers and settlers, a rotating disccontactor or a centrifugal contacter or any combination of these, issupplied at one end via line 12 with liquid furfural and at the otherend via line 14 with a suitable hydrocarbon oil, such as a gas oil, tobe solvent rened. There is removed overhead from the solvent refining ortreating tower 11 via line 15 a raffinate phase which is passed throughheat exchanger 16 and line 18 into rafiinate stripper 19 wherein it iscontacted with steam introduced thereinto via line 20. There is`recovered overhead from raffinate y 2,895,908 Patented July 2l, 1959ICC stripper 19 via line 21 a vaporous admixture of furfural, oil andwater, such as an azeotrope containing these materials, which is passedto condenser 22 wherein it 'is condensed and the resulting condensatepassed via line 24 into settling zone 25. Settling zone or settler 25 isprovided with compartments or suitable baffles therein to effect aseparation between the resulting condensed oil, water and furfural, thefurfural being most dense settling as the bottom phase, the water beingof intermediate density settling as the intermediate phase and the oilhaving the lightest density being the top phase. There is recovered fromthe bottom of rafiinate stripper 19 via line 26 solvent refined oil asproduct.

The extract phase comprised predominantly of furfural and more aromatichydrocarbons preferentially dissolved therein is recovered from solventrefining zone 11 via conduit 28 and passed through heater 29 and line 30into a rst vacuum flasher 31. There is recovered overhead from vacuumflasher 31 via line 32 a vaporous admixture of furfural and steamsubstantially free of oil. The liquid bottoms in vacuum flasher 31 isrecovered via line 34 and passed through heater 35 and line 36 into asecond vacuum flasher 38. There is recovered overhead from vacuumflasher 38 via line 39 a vaporous admixture of furfural and oil andco-boiling with furfural, and substantially no water.

The overhead vaporous admixture from vacuum flasher 31 is condensed incondenser 4t) and passed via line 41 into settler 42 wherein liquidfurfural settles from the Water. The water is removed from settler 42via line 44. The liquid furfural, containing a certain amount of waterdissolved therein but substantially free of oil, is removed from settler42 via line 45.

The overhead vaporous admixture from vacuum flasher 38 in line 39 iscondensed in condenser 46 to yield liquid furfural and oil substantiallyfree of water. The mixture of liquid furfural and oil from condenser 46is removed via line 48.

The liquid bottoms from vacuum flasher 38 is removed via line 49 andpassed through heat exchanger 50 and introduced via line 51 into extractstripper 52 wherein furfural is fractionally distilled by theintroduction of steam via line 54 into the lower portion of stripper 52.There is recovered overhead from stripper 52 via line 55 a vaporousadmixture of furfural, oil and water, such as a furfural-oil-Waterazeotrope, which is condensed in Condenser 56 and passed via line 58into settler 25. Settler 25 is provided to effect a separation betweenthe oil and Water and furfural therein. Settler 25, as previouslymentioned, is also employed as a settling zone for the overheadadmixture from rafiinate stripper 19. There isy recovered from settler25 via line 59 furfural substantially saturated (equilibrium amount)with water at the temperature at which settler 25 is operated. Thisfurfural also contains dissolved therein an equilibrium amount of oil.The furfural in line 59 is combined with the furfural in lines 45 and 48by means of line 60 and passed to furfural supply tank 6l. From supplytank 61 furfural is returned to the solvent rening zone 11 via lines 62and 12. From time to time, as needed, additional fresh furfural issupplied to the solvent refining zone 11 from an outside source, notindicated.

In the foregoing described operations, as previously indicated, thepractice of this invention is practcularly applicable to the solventrefining of gas oils, particularly gas oils containing aromatichydrocarbons or those hydrocarbons having a boiling point in the rangeSOO-500 F. and preferentially soluble in furfural.

The vacuum iiashers 31 and 38 may be operatedy at any suitableconditions to effect the desired separation. For example, both flashersmay be operated at a suitable absolute pressure in the range 5-700 mm.Hg. It

may be desirable to operate asher 31 at an absolute pressure greaterthan the absolute pressure in flasher 38 although suitable results arealso obtainable when the absolute pressure in iiasher 38 is the same asor greater than the absolute pressure in asher 31. Generally, the higherthe absolute pressure the higher the temperature required to effectflashing. Accordingly, it is desirable to operate these ashers in thelower absolute pressure range, such as at a pressure in the range -200mm. Hg, flasher 31 being operated at an absolute pressure in the range50-500 mm. Hg and flasher 38 at a lower pressure in the range 10-200 mm.Hg.

In the practice of this invention settling zones 25 and 42 and condenser46 are operated at a suitable convenient temperature, even, if desired,at substantially the same temperature. A temperature in the range 50-170 P. is usually adequate.

The solvent reiining zone, indicated as treating tower 11 in thedrawing, is operated under suitable conditions of temperature andpressure and solvent charge oil ratios to effect the desired separationand to maintain the resulting raffinate and extract phases immisciblewith respect to each other.

By operating a solvent refining process in the manner set forthhereinabove with reference to the drawing it is seen that the resultingcombined liquid furfural supplied via line 60 to furfural supply tank 61for use in the solvent refining operation contains less than theequilibrium amount of water and/ or oil dissolved therein. This isbrought about by virtue of the fact that the furfural recovered overheadfrom vacuum iiasher 38 via line 39 is substantially free of water and byvirtue of the fact that the furfural recovered overhead from vacuumasher 31 via line '32 is substantially free of oil. The furfuralrecovered overhead vial line 32 contains substantially all of the waterpresent in the extract phase removed from treating tower 11 via line 28and is separately recovered and discharded via line 44. Water issometimes employed admixed with the furfural in treating tower 11 toincrease or improve the selectivity of the selective solvent (furfural)for the more aromatic hydrocarbons in the charge oil. That amount offurfural recovered as liquid bottoms from vacuum flasher 38 via line 49is also recovered overhead from extract stripper 52 via line 55 andeventually from settling zone 25 via line 59. The furfural in line 59contains equilibrium amounts of water and oil dissolved thereindepending upon the temperature conditions at which settler 25 isoperated. However, the furfural contained in line 59 when admixed withthe furfural recovered via lines 45 and 48 contains less thanequilibrium amounts of oil and water, respectively. As a result ofcombining the furfural streams flowing in lines 59, 45 and 48 there issupplied to furfural supply tank 61 via line 60 a furfural stream havingless than an equilibrium amount of oil and water, respectively.

As will be apparent to those skilled in the art many changes,substitutions and modifications are possible in the practice of thisinvention without departing from the spirit or scope thereof.

I claim:

1. In an operation wherein furfural is employed as the selective solventfor the solvent refining of a hydrocarbon oil to yield a furfural richphase containing furfural and more aromatic hydrocarbons dissolvedtherein the improvement which comprises flashing said furfural richphase at a subatmospheric pressure to yield overhead a rst vapor streamsubstantially free of oil and comprising furfural and water and a firstliquid bottoms phase, subjecting said first liquid bottoms phase toashing at a subatmospheric pressure to yield overhead a second vaporstream substantially free of water and comprising furfural and oil and asecond liquid bottoms phase comprising substantially only furfural andoil, condensing said first vapor stream to separate liquid furfuraltherefrom, condensing said secondvapor stream, subjecting 4 said secondbottoms phase to distillation in the presence of steam to separateoverhead therefrom a vaporous admixture of oil, steam and substantiallyall of the furfural in said second bottoms phase, condensing theresulting overhead vaporous admixture to separate furfural therefrom,combining the furfural separated from said condensed rst vapor stream,the condensed second vapor stream and the furfural separated from saidcondensed vaporous admixture and employing the resulting combinedfurfural as selective solvent in the aforesaid solvent refining of saidhydrocarbon oil.

2. A process in accordance with claim 1 wherein said subatmosphericpressure is in the range 5-700 mm. Hg absolute.

3. A process in accordance with claim 1 wherein said hydrocarbon oilcontains hydrocarbons preferentially soluble in furfural and having aboiling point in the range 30G-500 F.

4. A process for solvent refining a hydrocarbon oil which comprisescontacting said oil with liquid furfural to form a ratfinate phase and afurfural-rich extract phase, subjecting said rainate phase to fractionaldistillation in the presence of steam to remove overhead a firstvaporous admiXture comprising furfural, oil and steam, and to yield arst liquid bottoms comprising substantially only solvent refined oil,dashing said extract phase at a subatmospheric pressure to yieldoverhead a first vapor stream substantially free of oil and comprisingfurfural and water and a second liquid bottoms phase, subjecting saidsecond liquid bottoms phase to flashing at a subatmospheric pressure toyield overhead a second vapor stream substantially free of water andcomprising furfural and oil and a third liquid bottoms phase comprisingsubstantially only furfural and oil, condensing said irst vapor streamto separate liquid furfural therefrom, condensing said second vaporstream, subjecting said third bottoms phase to distillation in thepresence of steam to separate overhead therefrom a second vaporousadmixture of oil, steam and substantially all of the furfural in saidthird bottoms phase, condensing said rst and second overhead vaporous-admixtures to separate furfural therefrom, combining the furfuralcondensed and separated from said first and second vapor streams withthe-furfural condensed and separated from said first aud second vaporousadmixtures and employing the resulting combined furfural as selectivesolvent in the aforesaid solvent refining of said hydrocarbon oil.

5. A process in accordance with claim 4 wherein said subatmosphericpressure is in the range 5-700 mm. Hg absolute.

6. A process in accordance with claim 4 wherein said hydrocarbon oil isa gas oil.

7. A process in accordance with claim 4 wherein said vaporous admixturesand said vapor streams are condensed and the resulting liquid furfuralseparated at a temperature in the range 50-170 F.

8. A process in accordance with claim 4 wherein said hydrocarbon oilcontains hydrocarbons preferentially soluble in furfural and having aboiling point in the range 30D-500 F.

9. A process in accordance with claim 4 wherein said rst and secondvaporous admixtures are condensed and the resulting liquid furfuralseparated from a common settling zone.

References Cited inthe leof this patent UNITED STATES PATENTS 2,186,298Kiersted et al. Jan. 9, 1940 2,526,722 Beavon Oct. 24, 1950 2,613,174Ockert Oct. 7, 1952 2,685,556 Hachmuth Aug. 3, 1954 2,742,400 Gross Apr.17, 1956 2,745,790 Manley May l5, 1956 2,809,222 Hawkins Oct. 8, 19,57

1. IN AN OPERATION WHEREIN FURFURAL IS EMPLOYED AS THE SELECTIVE SOLVENTFOR THE SOLVENT REFINING OF A HYDROCARBON OIL TO YIELD A FURFURAL RLICHPHASE CONTAINING FURFURAL AND MORE AROMATIC HYDROCARBONS DISSOLVEDTHEREIN THE IMPROVEMENT WHICH COMPRISES FLASHING SAID FURFURAL RICHPHASE AT A SUBATMOSPHERIC PRESSURE TO YIELD OVER HEAD A FIRST VAPORSTREAM SUBSTANTIALLY FREE OF OIL AND COMPRISING FURFURAL AND WATER AND AFIRST LIQUID BOTTOMS PHASE, SUBJECTING SAID FIRST LIQUID BOTTOMS PHASETO FLASHING AT A SUBATMOSPHERIC PRESSURE TO YIELD OVERHEAD A SECONDVAPOR STREAM SUBSTANTIALLY FREE OF WATER AND COMPRISING FURFURAL AND OILAND A SECOND LIQUID BOTTOMS PHASE COMPRISING SUBSTANTIALLY ONLY FURFURALAND OIL, CONDENSING SAID FIRST VAPOR STREAM, TO SEPARATE LIQUID FURFURALTHEREFROM, CONDENSING SAID SECOND VAPOR STREAM, SUBJECTINGG SAID SECONDBOTTOMS PHASE TO DISTILATION IN THE PRESENCE OF STEAM TO SEPARATEOVERHEAD THEREFROM A VAPOROUS ADMIXTURE OF OIL, STEAM AND SUBSTANTIALLYALL OF THE FURFURAL IN SAID SECOND BOTTOMS PHASE, CONDENSING THERESULTING OVERHEAD VAPOROUS ADMIXTURE TO SEPARATE FURFURAL THEREFROM,COMBINING THE FURFURAL SEPARATED FROM SAID CONDENSED FIRST VAPOR STREAM,THE CONDENSED SECOND VAPOR STREAM AND THE FURFURAL SEPARATED FROM SAIDCONDENSED VAPOROUS ADMIXTURE AND EMPOLYING THE RESULTING COMBINEDFURFURAL AS SELECTIVE SOLVENT IN THE AFORESAID SOLVENT REFINING OF SAIDHYDROCARBON OIL.